Modulation of human immune and inflammatory responses by dietary fatty acids.

I review the effects of the amount and composition of dietary fat on indices of human immune and inflammatory responses. A reduction in the amount of fat intake enhanced several indices of immune response, including lymphocyte proliferation, natural-killer-cell activity, cytokine production, and delayed-type hypersensitivity. When total fat intake was held constant, an increase in the intake of linoleic acid (18:2 omega-6) or arachidonic acid (20:4 omega-6) by healthy human volunteers did not inhibit many indices of immune response tested but did increase the production of inflammatory eicosanoids (prostaglandin E2 and leukotriene B4). Supplementation of human diets with omega-3 fatty acids reduced several aspects of neutrophil, monocyte, and lymphocyte functions, including the production of inflammatory mediators. Most of the studies have indicated reductions in these functions, with a minimum of 1.2 g/d of supplementation with eicosapentaenoic acid and docosahexaenoic acid for 6 wk. However, other studies concomitantly supplementing with 205 mg/d of vitamin E did not find inhibition of immune-cell functions, even with larger amounts and longer durations of supplementation with these fatty acids. One study reported that supplementation with docosahexaenoic acid selectively inhibits inflammatory responses without inhibiting T- and B-cell functions. Despite some discrepancies, fish oils have been used successfully in the management of several inflammatory and autoimmune diseases. The potential for the use of fish oils in the management of these diseases is tremendous, even though further studies are needed to establish safe and adequate intake levels of omega-3 fatty acids.